Six wash out consecutive sessions were carried out before starting the study with Fresenius FX8 Helyxone® , for patients who underwent HD, or with FX 80 Helyxone®, for patients who underwent hemodiafiltration (HDF). After the wash out period, fresh whole blood and serum samples were drawn on starting dialysis, during the midweek HD session for 4 consecutive weeks. For each patient the mean value of the 4 blood samples was considered. All patients continued HD or HDF with FX8 or FX 80 Helyxone® during the whole study period.In order to estimate the normal ranges of the parameters that we evaluated, 60 anonymous healthy volunteers were also submitted to the same assays.